[action-translation] Wire zh-cn sync automation and reconcile drift (Phase 0, Track B)

[mmcky]

Part of Phase 0 tracked in QuantEcon/action-translation#74. This repo is the English source for lecture-python.zh-cn, which holds 79 of 121 current lectures but has been dormant since 2025-11-26 — 40+ lecture PRs here (including the Kalman rewrites, Hansen–Singleton, unemployment dynamics, and the LQ permanent-income trilogy) have not flowed through, and 8 translated files still sit under pre-rename filenames.

Scope note: Phase 0 only reconciles the 79 already-translated lectures and turns automation on. Bulk translation of the 42 missing lectures and the restart of the RA review campaign are Phase 2 of the rollout (see QuantEcon/action-translation#74).

Todo

1. Repair the target repo so sync PRs can land correctly

• Rename the 8 orphaned files in lecture-python.zh-cn to match current source names (optgrowth.md → os.md, optgrowth_fast.md → os_numerical.md(?), cake_eating_problem.md/cake_eating_numerical.md, coleman_policy_iter.md, egm_policy_iter.md, ifp.md, mccall_correlated.md → verify each against the source rename history before moving)
• Regenerate heading-maps after the renames (translate headingmap)
• Clear the two stale review PRs [Non Conjugate Priors] Update Translations lecture-python.zh-cn#63 and [Rational Expectation] Update Translations lecture-python.zh-cn#87 (open since Sep/Oct 2025) — finish review and merge, or close, so the repo starts clean

2. Reconcile drift on the 79 translated lectures

• Generate an onboarding report against current HEADs (translate status / onboarding)
• Work through per-file drift decisions (source→target RESYNC vs backport vs manual); RESYNC drifted files with translate forward

3. Wire the automation (this repo)

• Add .github/workflows/sync-translations-zh-cn.yml, copied from lecture-python-programming with target-repo: QuantEcon/lecture-python.zh-cn (pin QuantEcon/action-translation@v0.15.0; include the \translate-resync comment trigger). Note: sync PRs for the 42 untranslated lectures will create new files — confirm desired behaviour with the action's docs-folder settings, or scope the workflow to existing files until Phase 2
• Confirm TRANSLATION_PAT and ANTHROPIC_API_KEY secrets are set on this repo

4. Review workflow (target repo)

• Add review-translations.yml and rebase-translations.yml to lecture-python.zh-cn, copied from lecture-python-programming.zh-cn (the target repo has a parked _future/ workflows folder — reconcile with what is there)

5. Verify end-to-end

• Trigger one sync on an already-translated lecture and confirm a translated PR opens, passes AI review, and builds in the target repo
• Tick off Track B in Phase 0 — wire sync automation into the two unwired zh-cn series (tracking) action-translation#74

[mmcky]

Track B wave executed 2026-07-18 with the post-#108 engine (CLI from action-translation main — no release contains #108 yet). Status against the todo:

1. Repair the target — done, staged: the 8 orphans resolved in QuantEcon/lecture-python.zh-cn#99 (5 renames verified against this repo's rename history — note optgrowth→os_stochastic and cake_eating_problem→os, not the mapping guessed above — plus 3 files deleted upstream in the cake-eating refactor, removed). Heading maps ship inside each resync PR (post-#108), so no separate headingmap pass is needed for resynced files. RA PRs zh-cn#63/#87: recommend merge first, their two files were excluded from the wave and get a follow-up resync so the RA improvements are preserved as ground truth.

2. Reconcile drift — done, staged: check-sync triage over all 79 mapped files (28 content-changed / 35 target-has-additions / 12 i18n-only / 4 identical), backward over the 35 (22 backport suggestions, incl. probable source bugs in ols (0.9) and ge_arrow (0.75) — will route via translate review), then a 62-PR forward wave: zh-cn#101–#162, localisation-swept (50 in-code Chinese lines restored across 9 branches; action-translation#107 validation reported upstream) and structurally verified.

3. Wire this repo — staged as #979 (pins @v0; carries the decision note about untranslated-lecture PRs once live). Secrets here verified: ANTHROPIC_API_KEY + QUANTECON_SERVICES_PAT both org-visible.

4. Target workflows — staged as zh-cn#100. Blocker: ANTHROPIC_API_KEY is not org-visible to the target repo — needs org admin. Also note the target's build-cache had expired (dormancy) — cache workflow re-enabled and a rebuild dispatched; wave-PR CI needs re-runs after it lands.

5. E2E verify — pending the merges + secret + a release containing action-translation#108 (@v0 is still v0.17.0; review mode can't see resync PRs until it moves).

Full run report and editor review guide (which doubles as the review-campaign restart scoping): project-translation reports/2026-07-18-intermediate-zh-cn-*.